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Abstract(Please copy/paste the abstract send to the congress) : |
Purpose:
Clinical use of multi detector computed tomography(MDCT) in diagnosis of diseases due to high
speed in data acquisition and high spatial resolution is significantly increased. Regarding to the
high radiation dose in CT and necessity of patient specific radiation risk assessment, the adoption
of new method in the calculation of organ dose is completely required and necessary. In this
study by introducing a conversion factor, patient organ dose in thorax region based on CT image
data using MC system was calculated.
Methods:
The geometry of x-ray tube, inherent filter, bow tie filter and collimator were designed using
EGSnrc/BEAMnrc MC-system component modules according to GE-Light-speed 64-slices CTscanner geometry. CT-scan image of patient thorax as a specific phantom was voxellised with
6.25mm3 in voxel and 64x64x20 matrix size. Dose to thorax organ include esophagus, lung,
heart, breast, ribs, muscle, spine, spinal cord with imaging technical condition of prospectivelygated-coronary CT-Angiography(PGT) as a step and shoot method, were calculated. Irradiation
of patient specific phantom was performed using a dedicated MC-code as DOSXYZnrc with
PGT-irradiation model. The ratio of organ dose value calculated in MC-method to the volume
CT dose index(CTDIvol) reported by CT-scanner machine according to PGT radiation technique
has been introduced as conversion factor.
Results:
In PGT method, CTDIvol was 10.6mGy and Organ Dose/CTDIvol conversion factor for
esophagus, lung, heart, breast, ribs, muscle, spine and spinal cord were obtained as; 0.96, 1.46,
1.2, 3.28. 6.68. 1.35, 3.41 and 0.93 , respectively.
Conclusion:
The results showed while, underestimation of patient dose was found in dose calculation based
on CTDIvol, also dose to breast is higher than the other studies. Therefore, the method in this
study can be used to provide the actual patient organ dose in CT imaging based on CTDIvol in
order to calculation of real effective dose(ED) based on organ dose. |